v.
1. tr. & intr. make or become hard or harder.
2 intr. & tr. become, or make (one's attitude etc.), uncompromising or less sympathetic.
3 intr. (of prices etc.) cease to fall or fluctuate.
Phrases and idioms:
harden off inure (a plant) to cold by gradual increase of its exposure.
Derivatives:
hardener n.